1. Field of the Invention
The present invention relates to a fuel injection system for mitigation of particle emissions from a vehicle during transient operating conditions, and more particularly to system and method for controlling fuel injection using a dual path fuel injection system that includes both port fuel injection and direct fuel injection.
2. Description of the Related Art
Fuel may be delivered to gasoline fuel internal combustion engines using a direct injection (DI) fuel system, a port fuel injection (PFI) fuel system, or a combination of these two systems. The combination of DI and PFI is referred to as a dual path fuel injection system. DI systems are widely known in the automotive industry for their particular advantages in high load. fuel efficiency. PFI systems are widely known for having low noise, vibration and harshness (NVH) at low load operating points, good fuel economy at low load operating points, and cost.
The emission of particulates from gasoline fuel internal combustion engines has become the focus of combustion development, due to more stringent legislation on the emissions of particle mass and particle number in Europe, North America, and China. A main source for the formation of particles in some engines with a DI portion 22 is the impingement of liquid fuel on the piston top. If the fuel does not evaporate rapidly enough, the fuel film will lead to a diffusion flame, that has been identified as a major source of soot (i.e. particle) formation. At a change in operation to a high load engine operation, the long injection duration leads to increased spray penetration, liquid fuel can impinge on the piston. If the engine stays at the high-load operating point for at least several seconds, the piston temperature will eventually rise high enough and the fuel that was deposited on the piston will evaporate before the main combustion event.
However, as the engine transitions from a low load point to a higher load operating point, the piston temperature will still be relatively cool and requires several seconds to heat up. Fuel that impinges on the piston immediately after the load step may not completely evaporate, and lead to diffusion flames on the piston top, also known as pool fires, forming and emitting large amount of particles.
Improved fuel injecting strategies are required to mitigate the emission of particles in transient engine operating conditions.